PROCESS GAS DECOMPOSITION REACTOR, invented by Bruce Minaee, filed May 17, 2000 and having SC/Ser. No: 09/572,111.
The present invention relates to the field of gas decomposition and, more particularly, to a microwave reactor for decomposing waste gases resulting from the manufacture of semiconductors and from other industrial processes.
Certain gases such as Perfluorinated Compounds (PFCs) including nitrogen trifloride, NF3, and sulfurhexafloride, SF6, and hydrofluorocarbons (HFCs) emitted by industrial processes, such as semiconductor processes, are harmful when released into the atmosphere. PFCs and HFCs are categorized as greenhouse gases because of their strong infrared absorption and long atmospheric lifetimes. PFCs and HFCs act similar to CO2 in causing the greenhouse effect. Because of their potential long term impact on the global climate, PFC""s, HFC""s, NF3 and SF6 have been included in the Kyoto Protocol which is aimed at significantly reducing the release of unwanted gases into the atmosphere.
The above-identified, cross-referenced application PROCESS GAS DECOMPOSITION REACTOR describes an improved microwave reactor for removing unwanted gases from industrial processes. In the cross-referenced application, a microwave reactor generates a plasma for decomposition of perfluorinated and hydro fluorocarbon compounds in a gas stream emerging from an industrial process, for example, a semiconductor manufacturing process. The reactor features a pair of magnetrons feeding a pair of launching waveguides to a pair of helical coils forming a microwave induction structure within a plasma chamber coaxial with the gas flow path.
In the cross-referenced application, the plasma chamber includes inlet and outlet openings through which reactant and additive gases (such as oxygen, hydrogen or water vapor) enter the chamber and exit the chamber for gas flow-through processing. The openings of the plasma chamber are through flanges which mate with corresponding flanges in exhaust gas lines from the industrial process apparatus. The gases enter the plasma microwave chamber through a standard vacuum flange, are dispersed, and undergo plasma decomposition reactions in the microwave chamber. The decomposition reactions result in hydrofluorocarbonated compounds and perfluorocarbonated compounds and these and other exhaust gases are evacuated from the plasma chamber through directly mounted flanges at the outlet of the plasma chamber.
In the cross-referenced application, decomposition reactions occur once the microwave chamber has been energized to cause a plasma and the reactant and additive gases are flowing. A microwave generated field causes ionization of the gas molecules by extracting electrons from them. These electrons are accelerated by the microwave generated field and cause more ionization and cracking of the gas molecules. The cracked reactant molecules and the cracked additive gas molecules react to form by-products that can be scrubbed by a wet scrubber.
While the cross-referenced application is a significant improvement over other gas reactors, the embodiments described are constrained by the ability to economically generate microwave-induced plasmas without excessive wear on the microwave components. As semiconductor processes use larger and larger gas-flow tubes for larger and larger semiconductor wafers and other parts, a need exists for larger, more efficient and more easily installed and maintained microwave reactors for removing unwanted gases.
Accordingly, there is a need for improved microwave reactors to decompose PFCs, HFCs and other unwanted gases suitable for insertion in the lines of processes used in industry, particularly in the semiconductor manufacturing industry.
The present invention is a microwave reactor for decomposing waste green house gases resulting from the manufacture of semiconductors and from other industrial. The microwave reactor includes a plasma chamber having a gas inflow port spaced apart from a gas outflow port for transporting gases through the plasma chamber. A gas plasma is generated in the plasma chamber to facilitate the gas decomposition. The structure of the microwave reactor includes an insulating cover protruding into the plasma chamber and forming an internal cavity that is isolated from gases in the plasma chamber. A microwave antenna extends into the internal cavity of the plasma chamber to couple the microwave energy into plasma chamber for causing a plasma to form in the gases. A microwave generator generates microwave power. A microwave connector connects the microwave power from the microwave generator to the plasma chamber. The microwave connector includes a microwave transport for transporting the microwave energy, a first microwave coupler for coupling the microwave energy from the microwave generator to the microwave transport with a matched impedance, and a second microwave coupler for coupling the microwave energy from the microwave transport to the plasma chamber with a matched impedance The second microwave coupler includes the microwave antenna extending into the internal cavity of the plasma chamber.
The foregoing and other objects, features and advantages of the invention will be apparent from the following detailed description in conjunction with the drawings.